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My mother had a mini-stroke a few weeks ago and was seen at the ER. The doctor gave her a prescription for a blood thinner. Her regular doctor was on vacation. She got a very big bruise on her arm last week and does not think she bumped it on anything; then today she got another one on her arm near her wrist. Both the bruises are on the right side, the side affected by her stroke. Were the bruises caused by the stroke or the blood thinner?

— Jean, Nevada

A stroke would not cause bruising. Blood thinners, however — such as coumadin and warfarin — have to be well controlled or they can lead to excessive bleeding, which might account for your mother's bruises. Bruising can also occur in older people after a minor, often unnoticed, trauma because of their fragile skin and vessels. This sensitivity is exacerbated by warfarin, which interferes with the blood's ability to clot. Although bruises may be unsightly, if there are no other signs of bleeding, they are usually not dangerous.

It is important for your mother to have regular blood examinations to be sure that her prothrombin time, or clotting time, is normal and not endangering her by causing either internal hemorrhage of any sort or external bruising. You should take her back to her doctor to have these tests done, and adjustments should be made in her blood thinner if the results are abnormal.